Interaction Between Methylene Blue and CalfThymus Deoxyribonucleic Acid by Spectroscopic Technologies |
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Authors: | Changlun Tong Zhou Hu and Jianmin Wu |
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Institution: | (1) Institute of Environmental Science, Zhejiang University, Hangzhou, 310029, China;(2) Department of Chemistry, Zhejiang University, Hangzhou, 310027, China |
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Abstract: | Characterization of the interaction between methylene blue (MB) and calf thymus deoxyribonucleic acid (ctDNA) was investigated
by UV absorption spectra, fluorescence spectra, fluorescence polarization and fluorescence quenching experiments by ferrocyanide.
The above results indicated that the binding modes of MB to ctDNA were relative to the molar ratio γ (γ=DNA]/MB]). At low
γ ratios (γ < 4), remarkable hypochromic effect with no shift of λmax in the absorption spectra of MB was observed in the presence of increasing amounts of ctDNA, the fluorescence of MB was efficiently
quenched by the ctDNA bases and the fluorescence polarization of MB was slightly increased, which indicated that MB cations
bound to phosphate groups of ctDNA by electrostatic interaction and then stacked on the surface of ctDNA helix. While at high
γ ratios (γ > 6), besides the fluorescence of MB was quenched efficiently by the ctDNA bases, a red shift (about 3 nm) in
the absorption spectra of MB was observed and the fluorescence polarization of MB was obviously increased, which indicated
the intercalation binding that MB molecules were intercalated into the space of two neighbouring DNA base pairs was the preferred
mode. Effects of K4Fe(CN)6 on the fluorescence quenching of the MB-ctDNA system at low and high γ ratios were also performed. The results showed that
at γ = 1.7, the quenching effect by ferrocyanide was higher than that of pure MB, while at γ = 13.6 a decreased quenching
of the fluorescence intensity was observed as compared with that of pure MB, which further proved the above conclusion. In
addition, the mechanisms of the hypochromic effect and the fluorescence quenching were also discussed in detail. |
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